CN113490559B

CN113490559B - Three-dimensional printing with blocked polyisocyanates

Info

Publication number: CN113490559B
Application number: CN201980093421.4A
Authority: CN
Inventors: T·陈
Original assignee: Hewlett Packard Development Co LP
Current assignee: Hewlett Packard Development Co LP
Priority date: 2019-03-22
Filing date: 2019-03-22
Publication date: 2023-10-31
Anticipated expiration: 2039-03-22
Also published as: EP3921103A4; US20220002586A1; CN113490559A; EP3921103A1; WO2020197540A1

Abstract

The present disclosure describes three-dimensional printing packages, systems for three-dimensional printing, and methods of three-dimensional printing. In one example, a three-dimensional printing kit may include a particulate build material and a binder. The particulate build material may include metal particles. The binder may include a polyol and a water-dispersible blocked polyisocyanate having a plurality of blocked isocyanate groups. The blocked isocyanate groups may include blocking groups bonded to carbon atoms of the blocked isocyanate groups via labile bonds that may be broken by heating to a deblocking temperature. Labile bond cleavage can produce a released blocking group that reacts with hydrogen and isocyanate groups.

Description

Three-dimensional printing with blocked polyisocyanates

Background

Three-dimensional (3D) printing may be an additive printing method for manufacturing three-dimensional solid parts from digital models. Three-dimensional printing is commonly used for rapid product prototyping, mold creation, master creation, and short-term manufacturing. Some 3D printing techniques are considered additive methods because they involve applying a continuous layer of material. This is different from other processes, which typically rely on removal of material to create the final part. Some 3D printing methods use chemical binders or adhesives to bond the build materials together. Other 3D printing methods involve partial sintering, melting, etc. of the build material. For some materials, partial melting may be achieved using heat assisted extrusion, and for other materials, curing or fusing may be achieved using, for example, ultraviolet light or infrared light.

Brief description of the drawings

FIG. 1 illustrates an exemplary three-dimensional printing package according to the present disclosure;

FIG. 2 illustrates an exemplary three-dimensional printing package after decapsulation in accordance with the disclosure;

FIG. 3 is a schematic illustration of a curing reaction of particulate build material with binder in an exemplary three-dimensional printing kit according to the present disclosure;

FIG. 4 is a diagrammatic view of a three-dimensional printing system according to the present disclosure; and

fig. 5 is a flow chart illustrating an exemplary three-dimensional printing method according to the present disclosure.

Detailed Description

The present disclosure describes three-dimensional printing suites, systems, and methods. In one example, a three-dimensional printing kit may include a particulate build material and a binder. The particulate build material may include metal particles. The binder may include a polyol and a water-dispersible blocked polyisocyanate having a plurality of blocked isocyanate groups having the chemical structure:

wherein B is a blocking group bonded to a carbon atom of the blocked isocyanate group via an labile bond that can be broken by heating to a deblocking temperature. The labile bond breaks to produce a released blocking group that reacts with hydrogen and isocyanate groups. In other examples, the metal particles may include titanium, cobalt, chromium, nickel, vanadium, tungsten carbide, tantalum, molybdenum, copper, gold, silver, iron alloys, stainless steel, high carbon steel, tool steel, alloys thereof, or mixtures thereof. In still other examples, the metal particles may have a D50 particle size distribution value of about 2 μm to about 100 μm. In certain examples, the water-dispersible blocked polyisocyanate may have an average of 3 to 10 blocked isocyanate groups per molecule. In other examples, the water-dispersible blocked polyisocyanate may include hydrophilic dispersing groups. In still other examples, the deblocking temperature may be about 100 ℃ to about 200 ℃. In some examples, the released blocking group may include a phenol, a pyridinol, a thiophenol, a mercaptopyridine, an alcohol, a thiol, a lactam, an oxime, an amide, an imide, an azole, an imidazole, a pyrazole, a diketene, a formate, or a combination thereof. In one particular example, the binder can include the polyhydroxy polyol in an amount of about 1 wt% to about 15 wt% and the water-dispersible blocked polyisocyanate in an amount of about 1 wt% to about 25 wt% relative to the total weight of the binder. In another example, the total moles of blocked isocyanate groups in the binder may be about 105 to 120 mole percent of the total moles of hydroxyl groups of the polyhydroxy polyol present in the binder.

The present disclosure also describes a system for three-dimensional printing. In one example, a system for three-dimensional printing may include a granular build material, a build material applicator for distributing a layer of the granular build material onto a support bed, and a fluid ejector connected to a binder and positioned to eject the binder onto the layer of granular build material. The build material may include metal particles. The binder may include a polyhydroxy polyol, and a water-dispersible blocked polyisocyanate having a plurality of blocked isocyanate groups having the chemical structure:

wherein B is a blocking group bonded to a carbon atom of the blocked isocyanate group via an labile bond that can be broken by heating to a deblocking temperature. The labile bond breaks to produce a released blocking group that reacts with hydrogen and isocyanate groups. In another example, the system may include a heater positioned to heat the layer of particulate build material and the binder on the layer of particulate build material to a deblocking temperature.

The present disclosure also describes a method of three-dimensional printing. In one example, a method of three-dimensional printing may include repeatedly applying a single layer of build material of a particulate build material comprising metal particles to a support bed. According to the 3D object model, a binder may be selectively applied to the individual layers of build material to define individually patterned layers that are bonded together to form the 3D green object. The binder may include a polyol and a water-dispersible blocked polyisocyanate having a plurality of blocked isocyanate groups having the chemical structure:

Wherein B is a blocking group bonded to a carbon atom of the blocked isocyanate group via an labile bond that can be broken by heating to a deblocking temperature. The labile bond breaks to produce a released blocking group that reacts with hydrogen and isocyanate groups. In one particular example, the adhesive may be applied by a hot fluid injector. In another example, the method may include heating the 3D green object to a deblocking temperature. The deblocking temperature may be about 100 ℃ to about 200 ℃. In yet another example, the method may further include sintering the 3D green object at a sintering temperature of about 500 ℃ to about 3,500 ℃ to fuse the metal particles together and form a sintered 3D object.

The three-dimensional (3D) printing materials and methods described herein may be used to form metallic 3D printed objects from metallic powder build materials. The 3D printing methods described herein may involve applying successive layers of particulate build material with a chemical binder or adhesive printed thereon to bond the successive layers of particulate build material together. In some methods, applying a binder may be employed to form a green object, and then a fused three-dimensional physical object may be formed therefrom. More specifically, a binder may be selectively applied to a layer of particulate build material on a support bed to pattern selected areas of the layer, and then another layer of particulate build material is applied thereon. The binder may be applied to the next layer of granular build material and these processes may be repeated to form a green part (also referred to as a 3D green body or object) which may then be heat fused to form a sintered 3D object.

Binders comprising polymers (e.g., water-soluble polymers or latex) may be used to bind the metal particles together to form a green body. The binder may comprise, for example, a liquid carrier and a polymeric binder. The polymeric binder may be dissolved or dispersed in a liquid carrier (e.g., an aqueous carrier) that is suitable for spraying from a fluid-spraying applicator. In some cases, the binder has been sprayed onto a layer of metal particulate build material and then heated sufficiently to evaporate water from the binder. After stacking a number of layers in this manner, a green body with a low water content can be formed, allowing the polymer from the binder to hold the metal particles together. However, in many cases, the green body can be very fragile at this point. The green body may be very porous and have many pores. Because the green body is fragile, it can be difficult to remove the green body from the surrounding powder in the powder bed without damaging the green body.

The present disclosure describes a binder comprising a polyol and a water-dispersible blocked polyisocyanate having a plurality of blocked isocyanate groups. Such binders can have good jetting properties because the polyhydroxy polyol and the water-dispersible blocked polyisocyanate are not polymerized as yet as the binder is jetted onto the particulate build material. The binder may be sprayed onto the layer of particulate build material, and the layer of particulate build material may then be heated to a deblocking temperature, such as a temperature of about 100 ℃ to about 200 ℃. In general, heating to the deblocking temperature may be performed on a single layer, or the green body may be first formed in bulk form, and then the entire green body may be heated to the deblocking temperature. At this deblocking temperature, the blocking groups of the isocyanate groups of the blocked polyisocyanate are removed. The isocyanate groups may then be reacted with the hydroxyl groups of the polyhydric polyol. Because the polyisocyanate molecule has multiple isocyanate groups, the polyisocyanate and the polyhydroxy polyol can react to form a crosslinked polymer network around the metal particles. The crosslinked polymer may make the green body stronger and more resistant to damage than other polymeric binders.

It is noted that when three-dimensional printing packages, methods of three-dimensional printing, and/or systems for three-dimensional printing are discussed herein, these discussions may be considered to apply to each other, whether or not they are explicitly discussed in the context of this example. Thus, for example, when discussing metal particles in relation to a three-dimensional printing suite, such disclosure is also relevant and directly supported in the context of a three-dimensional printing method, a system for three-dimensional printing, and vice versa.

It will be further understood that terms used herein will assume their ordinary meaning in the relevant art, unless otherwise indicated. In some cases, there are terms that are more specifically defined throughout the specification or that are included at the end of the specification, and thus, these terms may have the meanings described herein.

Three-dimensional printing set

In accordance with an example of the present disclosure, a three-dimensional printing kit 100 is shown in fig. 1. The three-dimensional printing kit may include a binder 106, and a particulate build material 110 that may contain metal particles 104. The binder, shown as droplets applied to the particulate build material in fig. 1 as an example, may be packaged or packaged with the particulate build material in a separate container, and/or the binder may be loaded with the particulate build material in a system for three-dimensional printing.

FIG. 2 shows build material 110 after the binder has been applied and heated to a deblocking temperature to form crosslinked polymer 206. The crosslinked polymer holds the metal particles 104 together. At this point, the metal particles bonded together by the crosslinked polymer may be a green body prepared for sintering, or additional layers of metal particles and binder may be added to form the green body. In some examples, a layer of metal particles may be sprayed with a binder and then heated to form a crosslinked polymer. In other examples, a single layer of metal particles may be sprayed with the binder without heating the layer to the deblocking temperature. The entire green body may be formed in this manner and subsequently heated to the deblocking temperature. In some cases, heating the entire green body to the deblocking temperature in this manner may further strengthen the green body by promoting cross-linking between individual layers of build material.

Build material

The build material contained in the three-dimensional printing kits described herein may be a particulate build material comprising metal particles. The particulate build material may include any type of metal particles that can be fused together at a fusion temperature (above the temperature at which the green body is formed, and above the deblocking temperature). Fusion may be performed by sintering, annealing, melting, etc. the metal particles in the particulate build material together. In one example, the particulate build material may include about 80 wt% to 100 wt% metal particles based on the total weight of the particulate build material.

In one example, the metal particles may be a single phase metal material composed of one element. In such an example, the fusing (e.g., sintering, annealing, etc.) may occur at a temperature below the melting point of the elements of the single-phase metallic material. In other examples, the build material particles may be composed of two or more elements, which may be in the form of a single-phase metal alloy (e.g., the various particles may be alloys), or may be in the form of a multi-phase metal alloy (e.g., the different particles may include different metals). In these examples, the fusing may generally occur over a range of temperatures. As for the alloy, a material having a metal alloy to a nonmetal (e.g., a metal-metalloid alloy) may also be used.

In some examples, the metal particles may include particles of elemental metals or alloys of titanium, cobalt, chromium, nickel, vanadium, tungsten carbide, tantalum, molybdenum, copper, gold, silver, iron alloys, stainless steel, high carbon steel, tool steel, alloys thereof, or mixtures thereof. In one example, the metal particles may be stainless steel.

The D50 particle size of the metal particles may be about 2 μm to equal to or less than about 100 μm. In some examples, the particles may have a D50 particle size distribution value, which may be about 10 to about 100 [ mu ] m, about 20 to about 100 [ mu ] m, about 15 to about 90 [ mu ] m, or about 50 to about 100 [ mu ] m. Individual particle sizes may be outside of these ranges, as "D50 particle size" is defined as the following particle size: at this particle size, half of the particles are larger than the D50 particle size and about half of the other particles are smaller than the particle size of the D50 particle size (by weight based on the metal particle content of the particulate build material).

As used herein, particle size may refer to the diameter value of a spherical particle, or in particles that are not spherical, may refer to the longest dimension of the particle. The particle size may appear as a gaussian or gaussian-like distribution (or a normal or normal-like distribution). The gaussian-like distribution is the following distribution curve: the profile may be Gaussian in its profile shape, but it may be slightly skewed in one direction or the other (toward the smaller or larger end of the particle size distribution range). That is, an exemplary gaussian-like distribution of metal particles may be generally characterized using "D10", "D50", and "D90" particle size distribution values, where D10 refers to the particle size at the 10 th percentile, D50 refers to the particle size at the 50 th percentile, and D90 refers to the particle size at the 90 th percentile. For example, a D50 value of 25 μm means that 50% of the particles (by number) have a particle size of more than 25 μm and 50% of the particles have a particle size of less than 25 μm. The particle size distribution value is not necessarily related to a gaussian distribution curve, but in one example of the present disclosure, the metal particles may have a gaussian distribution, or more typically a gaussian-like distribution with an offset peak at about D50. In practice, a true Gaussian distribution is not generally present, as there may be some skew, but a Gaussian-like distribution may still be considered as a "Gaussian" as used in practice. The particle shape of the particulate build material may be spherical, non-spherical, random, or a combination thereof.

Adhesive agent

The binder may include a polyol and a water-dispersible blocked polyisocyanate having a plurality of blocked isocyanate groups. The polyol may also be water dispersible. The blocked isocyanate groups may have the following chemical structure:

wherein B is a blocking group bonded to a carbon atom of the blocked isocyanate group via an labile bond that can be broken by heating to a deblocking temperature. The labile bond can be broken to produce a released blocking group that reacts with hydrogen and isocyanate groups. In other words, the C-B bond may be broken by heating to the deblocking temperature. the-B group abstracts the H atom bound to the N atom, becomes a released blocking group (BH) that reacts with hydrogen and forms an n=c double bond, yielding an isocyanate group (-n=c=o). After the isocyanate groups are deblocked in this manner, the isocyanate groups can react with the hydroxyl groups of the polyhydroxy polyol to form a polyurethane polymer. Multiple isocyanate groups on a single polyisocyanate molecule can react in this manner to form a crosslinked polyurethane polymer. In some examples, the water-dispersible blocked polyisocyanate may have an average of 3 to 10 blocked isocyanate groups per molecule.

In other examples, the blocked polyisocyanate may include hydrophilic dispersing groups to enhance the dispersibility of the blocked polyisocyanate in water. In some examples, the hydrophilic dispersing group may be anionic or nonionic. Non-limiting examples of hydrophilic dispersing groups may include polyethylene oxide, carboxylic acid groups or carboxylate groups, sulfonic acid groups or sulfonate groups, phosphonic acid groups or phosphonate groups, and the like.

The blocking group attached to the isocyanate group may be any group attached via an labile bond that can be broken by heating to a deblocking temperature. In certain examples, blocking groups (and/or released blocking groups BH that react with hydrogen) may include combinations thereof. In some examples, these blocking groups may be released from the isocyanate groups at a deblocking temperature of about 100 ℃ to 200 ℃. Various combinations of polyisocyanate compounds with different blocking groups may have different deblocking temperatures. In general, the deblocking temperature may be lower than the temperature at which the particulate build material sinters together.

One example of a suitable blocked polyisocyanate trimer has the structure shown below:

Wherein R is independently C2 to C10 branched or straight chain alkyl, C6 to C20 cycloaliphatic, C6 to C20 aromatic, or a combination thereof; and Z is (BL) _3-X (DL) _X Wherein BL is selected from the group consisting of a phenol blocking group, a lactam blocking group, an oxime blocking group, an azole blocking group, a diketene blocking group, a formate blocking group, and combinations thereof; x is 0 to 1; and DL is an anionic or nonionic hydrophilic dispersing group such as polyethylene oxide, carboxylic acid group, sulfonic acid group, or the like. Thus, Z independently comprises a blocking group (the "BL" group described herein), a hydrophilic dispersing group (the "DL" group described herein), or a combination of both. In some examples, the three independent Z groups shown in the above formula may represent 2 to 3 blocking groups (BL) and 0 to 1 hydrophilic dispersing groups (DL) per trimer molecule. Thus, in particular reference to Z in formula (la), there may be some specific single molecules of blocked polyisocyanates having three BL groups, as well as other single molecules comprising less than three BL groups. Thus, in some examples, no hydrophilic dispersing groups may be present, and in other examples, from 0.1 to 1 hydrophilic dispersing groups may be present.

Non-limiting examples of commercially available anionic water-dispersible blocked polyisocyanates include IMPLAFIX 2794 from Covesro (HDI trimer blocked with 3, 5-dimethylpyrazole and further comprising N- (2-aminoethyl) -beta-alanine ester; acid number 10 mg KOH/g) and BAYHYDUR BL XP 2706 from Covesro (blocked aliphatic polyisocyanate, acid number 32 mg KOH/g) (Covesro AG, germany). The IMPRAFIX 2794 can be decapsulated at about 130 ℃. Non-limiting examples of commercially available nonionic blocked polyisocyanates that may be used include Matsui FIXER ™ WF-N (3, 5-dimethylpyrazole nonionic blocked polyisocyanate) from Matsui Shikiso Chemical (Matsui Shikiso Chemical, japan) and TRIXENE Aquar BI 220 (nonionic aliphatic water dispersed blocked isocyanate) from Baxenden (Baxenden Chemicals Limited, UK). Matsui FIXER ™ WF-N can be unsealed at about 150 ℃. Additional examples of blocked polyisocyanates that may be used include BAYHYDUR (BL 2867), BAYHYDUR (BL 2781), BAYHYDUR (BL 5335), BAYYBOND (XL 6366) XP, BAYBOND (XL 825), BAYBOND (XL 7270), BAYBOND (XL 3674 XP), or VESTANAT (EP-DS 1205E) and VESTANAT (EP-DS 1076 (Evonik Industries AG, germany) from Covestro.

The polyol used in the binder may be any water-soluble or water-dispersible polyol. In some examples, the polyhydroxy polyol may include polyhydroxy polyesters, polyhydroxy polyurethanes, polyhydroxy polyethers, polycarbonate diols, and hydroxyl-containing polymers, such as polyhydroxy polyacrylates, polyacrylate polyurethanes, polyurethane polyacrylates, or combinations thereof. In other examples, the polyhydroxy polyol may be cationic, anionic, or nonionic. Non-limiting examples of commercially available polyhydroxy polyols that may be used include Bayhydrol A145, A2058, A2227/1, A242, A2427, A2542, A2546, A2601, A2646, A2651, A2695, AXP2770, A2845XP, A2846XP, U241, U355, U475, UXP2750, U2757, UXP2766, UXP7110E, and combinations thereof (Covestro AG, germany).

When the binder is applied to the particulate build material and then heated to a deblocking temperature, the blocked polyisocyanate may deblock and react with the polyhydroxy polyol to form a crosslinked polymer that binds the particulate build material together. Fig. 3 shows a schematic example of this method. In the figure, blocked polyisocyanate 310 is unblocked by heating at a unblocking temperature. The deblocked polyisocyanate 320 is then reacted with the polyol 330 in the presence of the particulate build material particles 340. The result is a crosslinked polyurethane polymer network 350 between and around particles of particulate build material that includes particulate build material associated with the reaction product of the deblocked polyisocyanate and the polyol. In some examples, such cross-linked polyurethane binders may impart greater strength to the green body than other types of binders, such as latex binders or water-soluble polymer binders. In certain examples, the binders described herein may be free of binders other than blocked polyisocyanates and polyhydroxy polyols. In other examples, the binder may be latex-free.

In some examples, the binder may include the polyhydroxy polyol in an amount of about 1 wt.% to about 15 wt.%, based on the total weight of the binder. In other examples, the binder may include the polyhydroxy polyol in an amount of about 2 wt.% to about 12 wt.%, or about 2 wt.% to about 10 wt.%, or about 4 wt.% to about 8 wt.%. In still other examples, the binder may include the water-dispersible blocked polyisocyanate in an amount of about 1 wt% to about 25 wt%, or about 2 wt% to about 20 wt%, or about 5 wt% to about 15 wt%. In certain examples, the amount of polyhydroxy polyol to water-dispersible blocked polyisocyanate may be selected based on the relative amounts of hydroxyl groups in the polyol and blocked isocyanate groups in the blocked polyisocyanate. In one example, the amounts of water-dispersible blocked polyisocyanate and polyol can be selected such that the binder comprises a molar excess of blocked isocyanate groups over hydroxyl groups. In some cases, the moles of the commercially available blocked polyisocyanate to the commercially available polyol can be calculated based on the equivalents provided by the manufacturer. In one particular example, the total moles of blocked isocyanate groups in the binder can be from about 105 mole% to 120 mole% of the total moles of hydroxyl groups of the polyhydroxy polyol present in the binder.

The binder may also comprise an aqueous carrier suitable for spraying. In one example, the aqueous carrier may comprise water as the primary solvent, e.g., the solvent is present at the highest concentration compared to other co-solvents. In addition to water, the aqueous carrier may include one or more organic co-solvents, such as high boiling solvents and/or humectants, for example, aliphatic alcohols, aromatic alcohols, alkyl glycols, glycol ethers, polyglycol ethers, 2-pyrrolidone, caprolactam, formamide, acetamides, and long chain alcohols. Some other more specific exemplary organic co-solvents that may be included in the binder may include aliphatic alcohols, 1, 2-alcohols, 1, 3-alcohols, 1, 4-alcohols, 1, 5-alcohols, 1, 6-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs of polyethylene glycol alkyl ethers (C6-C12), N-alkyl caprolactams, unsubstituted caprolactams, substituted formamides, unsubstituted formamides, substituted acetamides, unsubstituted acetamides, and combinations thereof. Examples of the water-soluble high boiling point solvent may include propylene glycol ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monobutyl ether, dipropylene glycol monophenyl ether, 2-pyrrolidone, 2-methyl-1, 3-propanediol, 1, 2-butanediol, 1, 4-butanediol, 1, 2-pentanediol, 1, 5-pentanediol, 1, 2-hexanediol, 1, 6-hexanediol, methyl pyrrolidone, ethyl pyrrolidone, and the like. The one or more organic co-solvents may add up to 0% to about 50% by weight of the binder. In some examples, the co-solvent may be present at about 5% to about 25%, about 2% to about 20%, or about 10% to about 30% by weight of the binder. In other examples, the co-solvent may be present in about 0 wt% to about 50 wt%, about 5 wt% to about 25 wt%, about 2 wt% to about 20 wt%, or about 10 wt% to about 30 wt% of the total solvent in the binder.

The aqueous carrier may be present in the binder from about 20 wt% to about 98 wt%, from about 70 wt% to about 98 wt%, from about 50 wt% to about 90 wt%, or from about 25 wt% to about 75 wt%. In some examples, the binder may further comprise from about 0.1 wt% to about 50 wt% of other liquid carrier components. These liquid carrier components may include other organic cosolvents, additives that inhibit the growth of harmful microorganisms, viscosity modifiers, pH adjusters, chelating agents, surfactants, preservatives, and the like.

Some examples of liquid carrier components that may inhibit the growth of harmful microorganisms that may be present may include biocides, fungicides, and other microbial agents. Commercially available examples may include ACTICIDE (Thor GmbH, germany), NUOSEPT (Troy, corp., new jersey), UCARCIDE ™ (Dow, michigan), VANCIDE (r.t. Vanderbilt co., ct), PROXEL (Arch Chemicals, inc., ct) and combinations thereof.

In other examples, the binder may also include a catalyst to promote polymerization of the polyisocyanate and the polyol. In certain examples, the catalyst may include tin carboxylates such as dibutyltin dilaurate or dibutyltin dioctoate, bismuth carboxylates, zinc carboxylates, chelates of zirconium and aluminum, tertiary amines such as triethylenediamine, N, N, N ', N ' ', N ' ' -pentamethyldiethylenetriamine, 1, 2-dimethylimidazole, or 1, 4-diazabicyclo [2.2.2] octane (DABCO).

The crosslinked polyurethane polymer formed from the binder may be subjected to a pyrolysis or burn-out process in which the polymer is removed during sintering or annealing. This may occur when thermal energy applied to the green part or object removes inorganic or organic volatiles and/or other materials that may be present either by decomposition or by burning the polymer.

System for three-dimensional printing

The present disclosure also extends to a system for three-dimensional printing. The system may generally include the particulate build material described above with a binder. The particulate build material may be distributed in a single layer by a build material applicator, and the binder may be sprayed onto the layer by a fluid sprayer. Fig. 4 shows an exemplary system 400 for three-dimensional printing according to the present disclosure. The system includes a build platform 402. Particulate build material 410 may be deposited onto the build platform by build material applicator 408, where the particulate build material may be leveled or smoothed, for example, by mechanical rollers or other leveling techniques. This may form a planar layer of particulate build material. The adhesive 406 may then be applied to the layer by fluid ejector 414. The area 424 to which the adhesive is applied may correspond to a layer or slice of the 3D object model. The system may also include a heater 412 that may apply heat to the layer of particulate build material and binder that has been applied. The heater may heat the build material and the binder to a deblocking temperature to initiate a reaction that produces the crosslinked polyurethane polymer, thereby binding the particulate build material together. This may form a solid green layer 426. In fig. 4, a green layer has been formed and then a new layer of particulate build material has been laid down on the first green layer. After jetting the individual layers with the binder, the build platform may be lowered a distance (x) that may correspond to the thickness of the printed layers to provide space for new layers of particulate build material. The figure shows the binder sprayed onto the new layer of particulate build material. After the green body is fully printed, the green body may be fused (e.g., sintered, annealed, etc.) in an oven 430.

As used herein, "applying a single layer of particulate build material onto a support bed" may include applying a first layer of particulate build material directly onto an empty support bed. The "support bed" may refer to a build platform, for example as shown in fig. 4. Further, in some examples, one or more layers of granular build material may be laid down on the support bed without spraying any binder onto the layers. This may provide a hotter uniform temperature distribution for the first layer to have adhesive sprayed thereon. Thus, "applying a single layer of particulate build material onto a support bed" may include applying a layer of particulate build material onto an initial layer or layers that may be applied without any binder. The phrase "applying individual layers of build material of particulate build material onto a support bed" also includes application to subsequent layers when layers or slices of green body have been formed in the underlying layers.

In other examples, the system may include a heater. The heater may be placed above the granular build material as in fig. 4, or in other examples, the heater may be on one or more sides of the granular build material, below the granular build material, or a combination of these locations. In some examples, the support bed may include an integrated heater to heat the granular build material from below. The heating may heat the particulate build material to a deblocking temperature to deblock the blocked polyisocyanate, and/or to a temperature sufficient to evaporate the solvent from the binder. In some examples, the heater may include a resistive heater, a heating lamp, an infrared heater, a halogen lamp, a fluorescent lamp, an oven, or other type of heater.

Three-dimensional printing method

A flowchart of an exemplary method 500 of three-dimensional (3D) printing is shown in fig. 5. The method comprises the following steps: repeatedly applying a single layer of build material comprising particulate build material of metal particles to a support bed 510; and selectively applying a binder to the individual layers of build material according to the 3D object model to define individually patterned layers that are bonded together to form a 3D green object, wherein the binder comprises:

polyhydroxy polyol, and

a water-dispersible blocked polyisocyanate having a plurality of blocked isocyanate groups having the chemical structure:

wherein B is a blocking group bonded to a carbon atom of the blocked isocyanate group via an labile bond that can be broken by heating to a deblocking temperature, wherein breaking the labile bond produces a released blocking group 520 that reacts with hydrogen and the isocyanate group. The particulate build material comprising metal particles and binder and related systems may be, for example, those previously described.

In more detail, repeatedly applying the single layer of build material of the particulate build material may include applying the single layer of build material at a thickness that may be from about 1 [ mu ] m to about 150 [ mu ] m, from about 20 [ mu ] m to about 150 [ mu ] m, from about 10 [ mu ] m to about 100 [ mu ] m, from about 25 [ mu ] m to about 75 [ mu ] m, from about 10 [ mu ] m to about 50 [ mu ] m, or from about 50 [ mu ] m to about 125 [ mu ] m. In some examples, the single layer of build material may have a thickness of about 1 μm to about 100 μm.

The adhesive may be selectively printed by a fluid ejector. In some examples, the fluid ejector may be a printhead, which may be a piezoelectric printhead, a thermal inkjet printhead, or a continuous inkjet printhead. After printing the individual layers of build material with the binder, in some cases, the individual layers of build material may be heated to drive off moisture and further cure the layers of the 3D green body. The build platform may be lowered by a distance (x) that may correspond to the thickness of the printed layer of the 3D green object so that another layer of granular build material may be added thereto, printed with a binder, cured, and the like. The process may be repeated on a layer-by-layer basis until the entire 3D green object is formed, which is stable enough to move to an oven suitable for fusing (e.g., sintering, annealing, melting, etc.).

In some examples, heat may be applied to a single layer (or group of layers) of build material having a binder printed on the single layer (or group of layers) of build material to drive off moisture from the binder and further cure the single layer of build material of the 3D green body. In other examples, the heat may be sufficient to heat the build material to a deblocking temperature to deblock the blocked polyisocyanate in the binder. In one example, heat may be applied from above the granular build material and/or may be provided by the build platform from below the granular build material. In some examples, the particulate build material may be heated prior to dispensing. In addition, the heating may be performed while applying the adhesive to the individual layers of build material or after applying all of the printed adhesive. One or more temperatures at which the metal particles of the particulate build material fuse together are higher than the ambient temperature of the patterned portion in which the 3D printing process is performed, e.g., patterning occurs at about 18 ℃ to about 300 ℃, and fusing occurs at about 500 ℃ to about 3,500 ℃. In some examples, the metal particles of the particulate build material may have a melting point of about 500 ℃ to about 3,500 ℃. In other examples, the metal particles of the particulate build material may be alloys having a range of melting points.

Thus, after forming the 3D green body, the entire 3D green body may be moved to an oven and heated to a temperature of about 500 ℃ to about 3,500 ℃, or more typically about 600 ℃ to about 1,500 ℃, in order to fuse the metal particles together and form a sintered 3D body. In some examples, the temperature may be about 600 ℃ to about 1,200 ℃, about 800 ℃ to about 1,200 ℃, or about 750 ℃ to about 1,500 ℃. In one example, depending on the metal particles, these temperature ranges may be used for the outer layer of the molten metal particles and may allow the metal particles to sinter to one another without melting the inner portion of the metal particles.

The final sintering temperature range may vary depending on the material, but in one example, the sintering temperature may be about 10 ℃ below the melting temperature of the metal particles of the particulate build material to about 50 ℃ below the melting temperature of the metal particles of the particulate build material. The sintering temperature may also depend on the particle size and the time for heating to occur, e.g., at an elevated temperature for a time sufficient to cause the particle surfaces to become physically fused or composited together. For example, the sintering temperature of the stainless steel may be about 1400 ℃, and examples of the sintering temperature of the aluminum or aluminum alloy may be about 550 ℃ to about 620 ℃. The sintering temperature may sinter and/or otherwise fuse the metal particles to form a sintered 3D object.

Definition of the definition

It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise.

The term "about" as used herein when referring to a value or range allows for some degree of variation of the value or range, for example within 10% of the limit of the value or range, or within 5% on the one hand. The term "about" when referring to a numerical range is also understood to include the range defined by the exact numerical value shown as a subrange of values, e.g., a range of about 1 wt.% to about 5 wt.% includes 1 wt.% to 5 wt.% as a explicitly supported subrange.

The phrases "green part," "green," "3D green object," and "layered green" as used herein refer to any intermediate structure prior to any fusing of particles with the particle material, including a 3D green object or one or more layers of a 3D green object, a green 3D support structure or one or more layers of a green 3D support structure, or an intermediate 3D separation interface or one or more intermediate 3D separation interface layers. As a green body, the particulate build material may be bonded together by a binder. Typically, the mechanical strength of the green body is such that the green body may be handled or extracted from the build platform for placement in a fusion oven. It should be understood that any particulate build material that is not patterned with a binder is not considered part of the green body, even if the particulate build material is adjacent to or surrounds the green body. For example, unprinted granular build material may be used to support a green body when received therein, but the granular build material is not part of the green body unless the granular build material is printed with a binder or some other fluid that is used to create a solidified part prior to fusing (e.g., sintering, annealing, melting, etc.).

The terms "3D part", "3D object" and the like are used herein to refer to a target 3D object to be built. The 3D object may be referred to as a "fused" or "sintered" 3D object, indicating that the object has been fused, such as by sintering, annealing, melting, etc., or as a "green body" or "green" 3D object, indicating that the object has solidified but has not yet been fused.

As used herein, a "kit" may be synonymous with and understood to include multiple compositions comprising multiple components, where the different compositions may be separately contained in the same container or containers prior to and during use (e.g., building a 3D object), but the components may be combined together during the building process. The container may be any type of vessel, box or receptacle made of any material.

The terms "fuse", "fusion" and the like refer to the joining of materials of adjacent particles of particulate build material, such as by sintering, annealing, melting, and the like, and may include the complete fusion of adjacent particles into a common structure, e.g., fused together, or may include surface fusion, where the particles are not completely fused to a liquefaction point, but are fused to the following points: which allows individual particles of the particulate build material to become bonded to one another, such as forming material bridges between the particles at or near the points of contact.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though the individual members of the list are identified as separate and distinct members. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list based on their presentation in a common group without indications to the contrary.

Concentrations, dimensions, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include the numerical values explicitly recited as the limits of the range, as well as to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and/or sub-range is explicitly recited. For example, a weight ratio range of about 1 wt% to about 20 wt% should be interpreted to include the explicitly recited limits of 1 wt% and 20 wt%, and to include individual weights such as about 2 wt%, about 11 wt%, about 14 wt%, and sub-ranges such as about 10 wt% to about 20 wt%, about 5 wt% to about 15 wt%, etc.

Examples

Embodiments of the present disclosure are shown below. However, it is to be understood that the following are illustrative of the application of the principles of the present disclosure. Many modifications and alternative compositions, methods, and systems may be devised without departing from the spirit and scope of the present disclosure. The appended claims are intended to cover such modifications and arrangements.

A series of struts are formed from stainless steel powder and a binder. The stainless steel powder and the binder are mixed with a high speed mixer to ensure uniform mixing. The wet powder was dried in a vacuum oven at 30 ℃ for two hours until approximately 80% of the water was removed. 18 grams of this dry powder was poured into the opening of a compression bar mold and compressed at 2000 psi for 30 seconds to form compression bars (50 mm (length), 12mm (width) and 5.5mm (thickness)). The struts were carefully separated from the mold and cured with a slow air stream at 180 ℃ for 30 minutes at a pressure of 22-25 inches hg in a vacuum oven. The solidified struts were cooled and sent to a 3-point bending Instron tester to measure tensile strength.

Several different binder formulations were used to make the struts to compare the tensile strength of the resulting struts. Five struts were made for different strut formulations and the average maximum tensile stress (mPa) and standard deviation were reported.

The blocked polyisocyanate included in the binder formulation was the Imprafix (r) 2794 blocked isocyanate dispersion of Covestro (40% solids in water,% NCO 4.8%). Polyols are different in different formulations. The polyol is from Bayhydrol polyol series based on water. The Bayhydrol polyols used are shown in Table 1.

TABLE 1

Bayhydrol polyol	Type(s)	% solids	%OH	Equivalent weight of
					A 2546	Acrylic polyols	41	4.8	354
A 2601	Acrylic polyols	45	3.9	436
					A 2542	Acrylic polyols	50	3.8	447
A 2695	Acrylic polyols	41	5	340
					A 2846	Acrylic polyols	40	1.5	1133
A2646	Acrylic polyols	50	3.8	447
					UXP 2750	Polyurethane polyols	41	3.6	472
UXP 2766	Polyurethane polyols	37	4	425
					U 2757	Polyurethane polyols	52	1	1700

Various binder formulations are shown in table 2. 10 wt% of the Imprafix 2764 is used as blocked polyisocyanate in the formulation. In various formulations, the polyols were different and the amount of polyol was calculated based on the% OH of the polyol reported by the manufacturer such that there was a 10 mole% excess of NCO compared to the moles of OH.

TABLE 2

Ink setNumber of sample/sample	% active	1 (Compound)	2 (Compound)	3	4	5	6	7	8	9	10
												1, 2-butanediol	As is	26.0	26.00	26.0	26.0	26.0	26.0	26.0	26.0	26.0	26.0
Tergitol® 15-S-7	100	0.90	0.90	0.90	0.90	0.90	0.90	0.90	0.90	0.90	0.90
												Tergitol® TMN-6	90	0.90	0.90	0.90	0.90	0.90	0.90	0.90	0.90	0.90	0.90
Cyan ink	12.72	0.40	0.40	0.40	0.40	0.40	0.40	0.40	0.40	0.40	0.40
												Reaxis® C708	100	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01	0.01
Latex	32	10
												Imprafix® 2794	38.0		10.00	10.0	10.0	10.0	10.0	10.0	10.0	10.0	10.0
Bayhydrol® A-2646	50.0			4.26
												Bayhydrol® UXP 2766	37.0				4.05
Bayhydrol® U XP 2750	41.0					4.50
												Bayhydrol® A 2695	41.0						3.24
Bayhydrol® A-2546	41.0							3.38
												Bayhydrol® A2601	45.0								4.15
Bayhydrol® A 2542	50.0									4.26
												Bayhydrol® A2846	40.0										10.75

The amounts shown in table 2 are parts by weight as dry content (i.e. the ingredients do not include any water content). Water was then added to obtain a total of 100 parts by weight. The cyan ink was used to visualize the powder mix quality. Imprafix cube 2794 is a commercial blocked isocyanate dispersion from Covestro Chemical Company.

Tergitol 15-S-7 and TMN-6 are surfactants from Dow (Michigan).

Reaxis C708 is a Bi-Zn promoter for polyurethane polymerization from Reaxis, inc.

The compression bar formulation contained 94.8 wt% stainless steel powder and 5.2 wt% binder. The stainless steel powder used in this study was PAC #1009 having an average particle size of 22 μm. Table 3 shows the maximum tensile stress and standard deviation of the cured struts (5 struts with associated adhesive formulations were tested and averaged for maximum tensile stress).

TABLE 3 average maximum tensile stress of the cure struts (cure temperature=180℃)

Sample number	Latex (wt.%)	Imprafix 2764 (wt.%)	Polyol (wt%)	Polyhydroxy polyol	Maximum strength of	STD
							1 (Compound)	10	0	0	Without any means for	4.0	0.1
2 (Compound)		10	0	Without any means for	4.84	0.20
							3		10	4.26	Bayhydrol® A-2646	7.41	0.24
4		10	4.05	Bayhydrol® UXP 2766	11.80	0.35
							5		10	4.5	Bayhydrol® U XP 2750	6.60	0.32
6		10	3.24	Bayhydrol® A 2695	9.31	0.48
							7		10	3.38	Bayhydrol® A-2546	9.19	0.25
8		10	4.15	Bayhydrol® A2601	10.46	0.46
							9		10	4.26	Bayhydrol® A 2542	7.64	0.47
10		10	10.75	Bayhydrol® A2846	10.16	0.49

Based on these test results, the reaction product of Imprafix 2764 with bayhydro l polyhydroxy polyol can be a very strong binder for metal powders. The formulation tested was stronger than the latex binder used in comparative sample 1. The formulation tested was also stronger than comparative sample 2 (which included Imprafix cube 2764 without any polyol). Of the formulations tested, bayhydrol UXP 2766, A2695, A-2546, A-2601 and A2846 gave the best results, but all formulations were superior to the control samples.

Claims

1. A three-dimensional printing kit comprising:

a particulate build material comprising metal particles; and

a binder, comprising:

polyhydroxy polyol, and

wherein B is a blocking group bonded to a carbon atom of the blocked isocyanate group via an labile bond cleavable by heating to a deblocking temperature, wherein cleavage of the labile bond results in a released blocking group that reacts with hydrogen and the isocyanate group,

wherein the total moles of blocked isocyanate groups in the binder is from 105 mole% to 120 mole% of the total moles of hydroxyl groups of the polyhydroxy polyol present in the binder.

2. The three-dimensional printing kit of claim 1, wherein the metal particles comprise titanium, cobalt, chromium, nickel, vanadium, tungsten, tantalum, molybdenum, copper, gold, silver, iron alloys, or mixtures thereof.

3. The three-dimensional printing kit of claim 1, wherein the metal particles comprise steel.

4. The three-dimensional printing kit of claim 1, wherein the metal particles comprise stainless steel, high carbon steel, tool steel, or mixtures thereof.

5. The three-dimensional printing kit of claim 1, wherein the metal particles have a D50 particle size distribution value of 2 μιη to 100 μιη.

6. The three-dimensional printing kit of claim 1, wherein the water-dispersible blocked polyisocyanate has an average of 3 to 10 blocked isocyanate groups per molecule.

7. The three-dimensional printing kit of claim 1, wherein the water-dispersible blocked polyisocyanate comprises hydrophilic dispersing groups.

8. The three-dimensional printing kit of claim 1, wherein the deblocking temperature is 100 ℃ to 200 ℃.

9. The three-dimensional printing kit of claim 1, wherein the released blocking group comprises a phenol, a mercaptopyridine, an alcohol, a thiol, a lactam, an oxime, an amide, an imide, an azole, a diketene, a formate, or a combination thereof.

10. The three-dimensional printing kit of claim 1, wherein the released blocking group comprises a pyridinol, thiophenol, imidazole, pyrazole, or a combination thereof.

11. The three-dimensional printing kit of claim 1, wherein the binder comprises the polyhydroxy polyol in an amount of 1 wt% to 15 wt% and the water-dispersible blocked polyisocyanate in an amount of 1 wt% to 25 wt%, relative to the total weight of the binder.

12. A system for three-dimensional printing, comprising:

a particulate build material comprising metal particles;

a build material applicator for distributing a layer of particulate build material onto a support bed;

a fluid injector fluidly connected to a binder and positioned to inject the binder onto a layer of particulate build material, wherein the binder comprises:

polyhydroxy polyol, and

13. The system for three-dimensional printing of claim 12, further comprising a heater positioned to heat the layer of particulate build material and the binder on the layer of particulate build material to an unsealing temperature.

14. A method of three-dimensional printing comprising:

repeatedly applying individual layers of build material of a particulate build material comprising metal particles to a support bed;

according to a 3D object model, a binder is selectively applied to individual layers of build material to define individually patterned layers that are bonded together to form a 3D green object, wherein the binder comprises:

polyhydroxy polyol, and

15. The method of three-dimensional printing of claim 14, wherein the adhesive is applied by a hot fluid ejector.

16. The method of three-dimensional printing of claim 14, further comprising heating the 3D green object to a deblocking temperature, wherein the deblocking temperature is 100 ℃ to 200 ℃.

17. The method of three-dimensional printing of claim 14, further comprising sintering the 3D green object at a sintering temperature of 500 ℃ to 3,500 ℃ to fuse metal particles together and form a sintered 3D object.